The main objectives of the study are a) to assess the extent of worsening/relapse upon discontinuation of imipramine and to test the hypothesis that maintenance on the drug protects from such reversal in a total experimental sample of 100 subjects with Panic Disorder and Agoraphobia who have shown good and stable response to 6 months of systematic open treatment prior to randomization to the 12 month prospective placebo controlled discontinuation/maintenance phase of the study; b) An evaluation of late relapse/reversals achieved by extending the observation period of the double-blind placebo substitution condition to 24 months; c) A controlled assessment of relapse within the 12 month period following discontinuation of 1 year maintenance treatment d) A follow-up for 3 to 4 years from initial randomization of study completers and relapsers who are retreated as well as subjects who drop out from various stages of the double-blind protocol in order to gather systematic longitudinal and clinically relevant data specifically as they relate to relapse after varying lengths of imipramine maintenance treatment.